A number of commercially available analgesic products are flavoured. Among such products commercially available in the UK are BOOTS Cold Relief Hot Blackcurrant/Lemon and the LEMSIP range from Reckitt Benckiser (registered trade marks). Analgesic products flavoured with fruit flavorants, especially those reproducing sharp flavours such as blackcurrant and lemon, have excellent consumer acceptance.
However the incorporation of flavorants is not absolutely straightforward. Most flavorants are oil-based and are moderately volatile. Many tablets are made by a process which includes wet granulation, involving a drying step. If an oil-based flavorant is present during the drying step it may be lost, completely or in part. Furthermore, when analgesic tablets contain paracetamol as the (or an) active ingredient the process is inherently difficult; paracetamol is, simply, a difficult material to tablet. When an oil-based flavorant is added to paracetamol, it tends to increase the difficulties in tabletting; the oleophilic qualities of the flavorant act to increase the difficulty in getting particles to adhere together.
Thus, in an internet article called “New Opportunities—Speciality Pregelatinised Starch Excipients” by Dr F Heinze, at: www.samedanltd.com/members/archives/PMPS/Autumn2002/FredHeinze.htm
Dr Heinze states “Wet granulation is the chosen method for poorly compressible drugs such as Acetaminophen (paracetamol)”.
Additionally, U.S. Pat. No. 4,562,024 concerns an improved wet granulation process for preparing compressed tablets, particularly those containing a “poorly compressible medicament e.g. paracetamol”.
In the British Pharmaceutical Society (BPS) 2005 Science Abstracts, Abstract 212 which is available online at www.rpsgb.org.uk/pdfs/bpc05sciabs204-212.pdf; called “An Investigation into the Recrystallization Behaviour of Amorphous Paracetamol”, the authors S. Qi and D. Q. M. Craig, of the School of Chemical Sciences and Pharmacy, University of East Anglia, UK, state that paracetamol is known to exist in three polymorphic forms, including the stable monoclinic form I which has “poor tabletting properties”.
Thus, starting points for the present invention are that paracetamol is difficult to tablet, and that paracetamol tablets are conventionally made by a wet granulation process; consequently flavorants are difficult to incorporate. Adding them too early in the manufacturing process causes loss of flavorant.